An Affordable Lithium Boat Battery

[Kelpie]

I don't actually plan to remove the lead acid system. It has a fairly charmed life, with very little load on it and 230w of solar plus the engine feeding it. So I expect the batteries to last a long time. They're not really doing any harm.

One change I will be making is to, finally, have a way of charging the lithium from the engine. I'm installing a small (18A) Victron Orion to charge the new windlass (LA) battery, and I think I will set it up so that I can swap it across to the big lithium bank. It will require a setting change in the app and physically changing connections, but I envisage it as an emergency/backup thing only.
I've managed two years full time without needing anything except solar but if I'm buying another blue box I might as well get my money's worth out of it.

I did attempt to install a 60A Sterling DC-DC charger but for whatever reason it didn't work. It was pretty big anyway, I don't think long term my alternator would have been happy.

 

[noelex]

100+ posts in and nobody has even mentioned our solution to the problem. (We expected howls of outrage and have been hiding behind the sofa in anticipation...)

Lithium systems have major advantages, but they do also have drawbacks that should be taken into account. One of the major drawbacks is the necessity for complicated electronic systems to monitor the battery and the concern that these systems could shut the battery supply down with little warning and possibly at an inopportune moment.

It is a valid concern.

Your system eliminates one of the major protection systems, but this also eleminates the chance of an inadvertent shut down if there is a fault in this protection system. There is no automatic shut down to protect the battery if during discharge one or more of the cells drops below a safe voltage level. You have installed protection on the charging side only. This means that a fault in the BMS electronics cannot shut your house system down, but if a cell does drop below the safe voltage level the house system will still eventually shut down anyway and the battery will be permanently damaged. This could not be be fixed without replacement of at least one cell.

With most lithium systems with the protection of a BMS on the discharge side the fault is usually easily cleared by starting one of the charge sources. No permanent damage to the battery would result. If the BMS itself became faulty, this could be bypassed, although this requires some electrical knowledge.

I can understand why you have made the choices you have. It is a valid option for people to consider, providing they understand the advantages and drawbacks.

I am a firm believer in the KISS principal when outfitting a cruising boat so your solution has some appeal, but the compromises would not suit our boat. The thought of being halfway across the Atlantic is no house battery and no way to repair the fault or jury rig a fix would not be acceptable. However, you have correctly pointed out that your solution is not designed for blue water boats so you make this limitation perfectly clear.

In summary, I don’t think the solution you have presented is better or worse, just suited to some boats and not others.

An improvement that may be worth incorporating is an audible alarm if the voltage of one cell approaches a damaging level during discharge.

One disclaimer I would make clear with your system is once a lithium cell has been discharged below a safe level it becomes dangerous to continue to use that cell even if the voltage can be restored. This warning should be made clear to anyone installing your system.

 

[Zing]

By introducing a disconnect switch, lithium systems have actually taken a giant step backwards compared to lead as:

* Battery current delivery is throttled and the battery's source resistance increased

* A single point of failure has been added to the boat's primary circuit (no doubt relying on cheap and/or fake Chinese mosfets)

* An automatic control system with the authority to disconnect everything has been introduced (often with ill-designed and low quality software)

* The switch produces waste heat (i.e. efficiency losses and hot components), and switches with a reasonable current rating need fan cooling (i.e. fan failure and dust build up issues)

Systems like a REC BMS plus a Blue Sea contactor go someway to mitigate the above, but that solution is very expensive. Nevertheless, it's probably the only commercial system we would trust to keep the lights on.

100+ posts in and nobody has even mentioned our solution to the problem. (We expected howls of outrage and have been hiding behind the sofa in anticipation...)

PS. Please don't ask 'What is your solution?' as it's set out in the link on post #1

I agree a separate disconnect contactor/relay is better than one built into the board. I also couldn't find a large enough BMS for my loads with an on-board current disconnect anyway.

The disconnect switch or rather the BMS controlling it is indeed a considerable increase in risk. I think it is good to have a BMS by-pass switch and means to switch off the BMS very quickly if it has shut you down for no good reason. I have installed that.

Even better would be to have parallel banks in addition, so if one BMS went haywire, you should still have another working.

 

[Kelpie]

I agree a separate disconnect contactor/relay is better than one built into the board. I also couldn't find a large enough BMS for my loads with an on-board current disconnect anyway.

The disconnect switch or rather the BMS controlling it is indeed a considerable increase in risk. I think it is good to have a BMS by-pass switch and means to switch off the BMS very quickly if it has shut you down for no good reason. I have installed that.

Even better would be to have parallel banks in addition, so if one BMS went haywire, you should still have another working.

How big are your loads?

 

[Zing]

How big are your loads?

Intermittently >600A

 

[katy_Stickland]

A couple of years ago we looked into upgrading our failing AGM house batteries to lithium, but unfortunately the price of a commercial system was somewhat beyond our budget. Nevertheless, we wondered whether a diy approach would bring the cost down to an affordable level and started investigating. Published designs didn’t seem to meet our needs, but by taking a fresh approach and challenging some received wisdom we came up with our own design; an affordable solution that works well. We’ve been enjoying the benefits of Lithium for more than two years now, and our system has proved both reliable and effective. Here is the story; we hope it is of interest. bit.ly/43D3X1h

Hi Migs, would you be happy for the article to be published in Practical Boat Owner magazine? If so, please do email me direct: katy.stickland@futurenet.com, Thanks, Katy Stickland

 

[Kelpie]

Intermittently >600A

Sounds like a good place to use lead acid!

 

[Zing]

Sounds like a good place to use lead acid!

Lead is dead.

 

[Kelpie]

Lead is dead.

It's still the best option for engine start, IMHO. Unless you really need to save 10kg and that's the only way you can do it.

 

[Buck Turgidson]

Buying direct from China at least bypasses the need to ignore safety recalls

 

[Kelpie]

Buying direct from China at least bypasses the need to ignore safety recalls

I feel much more confident buying cells and a BMS and then balancing and assembling it all myself, so that I have intimidate knowledge of every component and connection, than I would with buying any 'drop in' sealed box with unknown internals.

 

[Buck Turgidson]

I feel much more confident buying cells and a BMS and then balancing and assembling it all myself, so that I have intimidate knowledge of every component and connection, than I would with buying any 'drop in' sealed box with unknown internals.

I'm all for it! But you haven't taken the cells apart to inspect them so you have no idea of the quality.

 

[geem]

I'm all for it! But you haven't taken the cells apart to inspect them so you have no idea of the quality.

But if you buy from a reputable European or British supplier you have some come back that you never get buying from China. Having said that, mine came from the USA warehouse of a Chinese supplier. The cells, so far have been excellent. The next cells are coming from a different USA based company with certification.

 

[Kelpie]

I'm all for it! But you haven't taken the cells apart to inspect them so you have no idea of the quality.

Yes you can't take them apart without destroying them. So you have to plump for a supplier who had a good track record.
Fortunately it seems almost impossible to install lithium without shouting about it from the rooftops, so there's plenty of first hand experiences out there on forums and social media.

 

[gregcope]

I'm all for it! But you haven't taken the cells apart to inspect them so you have no idea of the quality.

The Ali case Eve L280K and L304 cells are UL listed amongst other standards so would be suitable for use in a ABYC standard build. Most assemblers (inc some DIYers) do a discharge test of both the cells and the whole battery. These cells are also used by other manufacturers (European and US) although most are assembled in Asia. On most boats they have a relatively easy life in terms of temperature, charge rates / discharge depth, cycles and Shock compared to their data sheets or other use cases (e.g. RVs).

So I would surmise that the cells are of decent quality if purchased from a reputable supplier/reseller. If not I would expect lots of people to have complained and had issues by now considering their relative prevalence.

 

[gregcope]

In terms of issues with BMS (specifically MOSFET ones) I agree with @Kelpie and @geem.

The BMS I chose is rated at 200A continuous. I have downgraded it to 175A. Tested under load and inspected connections for heat and resistance pre, during and post test. Its got a massive heak sink. Yes it could fail. I have two and spares. The model I use is sold globally and in use on multiple other commercial batteries. I would expect failures to be common knowledge by now. Yes there could be a software issue in due course however these have no knowledge of dates so this would be some other latent issue. The software is probably used on all BMS of this sort (irrespective of size) by the manufacture so is on lots of them. Yes MOSFETs will not last forever. However many last a very long time (in my experience longer than say capacitors), especially if gently loaded.

I also still have a FLA starter battery I can switch in.

In terms of a disconnect, should we not, as good sailors plan for that anyway? I have had that happen with two FLA batteries that dropped to below 10V which caused most things to shutdown. Both had internal shorts, got extremely hot and were venting H2S. One of these events was when I was sailing. I have since rewired to make my boat much safer with individual isolators, fuses and connectors as well as temp alarm(s) so that it is easy to isolate an errant battery.

 

[jakew009]

If you are worried about a BMS cutting out at an inopportune time, why not wire all your critical loads (navigation etc) to a changeover switch that is connected to the lithium bank and your lead acid starter battery?

That way if you 'lost' the lithium bank for any reason, a single changeover switch would have the important stuff running off the starter bank and charged by the alternator in seconds.

 

[geem]

If you are worried about a BMS cutting out at an inopportune time, why not wire all your critical loads (navigation etc) to a changeover switch that is connected to the lithium bank and your lead acid starter battery?

That way if you 'lost' the lithium bank for any reason, a single changeover switch would have the important stuff running off the starter bank and charged by the alternator in seconds.

We have that and also a second lead battery bank. Its a sensible set up. Oversizing your starter battery for such an eventuality would also make sense, so it can take some additional load.

 

[noelex]

If you are worried about a BMS cutting out at an inopportune time, why not wire all your critical loads (navigation etc) to a changeover switch that is connected to the lithium bank and your lead acid starter battery?

That way if you 'lost' the lithium bank for any reason, a single changeover switch would have the important stuff running off the starter bank and charged by the alternator in seconds.

You need to also consider the damage to other equipment if the BMS should disconnect the battery supply unexpectedly.

It is not enough to simply switch over to the starter battery or carry a replacment BMS. Provision also needs to made to prevent damage of other equipment should this type of disconnection occur. There are mechanisms to prevent this damage, but this issue is often not considered adequately.

One major advantage of Migs’ system is that these protective mechanisms are not used on the output side. There is no discharge protection mechanism and therefore no risk of damage to electronics from a disconnection due to a discharge problem. However, the charge system can still unexpectedly disconnect and this will potentially cause some damage to charge sources. The problem is reduced, but it is not eliminated.

 

[jakew009]

You need to also consider the damage to other equipment if the BMS should disconnect the battery supply unexpectedly.

It is not enough to simply switch over to the starter battery or carry a replacment BMS. Provision also needs to made to prevent damage of other equipment should this type of disconnection occur. There are mechanisms to prevent this damage, but this issue is often not considered adequately.

One major advantage of Migs’ system is that these protective mechanisms are not used on the output side. There is no discharge protection mechanism and therefore no risk of damage to electronics from a disconnection due to a discharge problem. However, the charge system can still unexpectedly disconnect and this will potentially cause some damage to charge sources. The problem is reduced, but it is not eliminated.

Can you give me an example of what equipment will be damaged if the BMS suddenly disconnects?

Ignore the alternator as that is better connected to the starter bank and charging the lithium bank with a dc/dc converter.